Photographs have in general been regarded as mediums that "do not lie." However, the inherent trustworthiness of photographs have been compromised by the increasing sophistication and ease with which photographic images can be manipulated. This problem is particularly severe in the case of digital cameras which store a recorded image in digital memory, such as on magnetic tape or laser disc instead of photographic film. There the concept of an "original" image is no longer meaningful.
While a need for authenticating photographs exists today, the seriousness of the problem is not yet widely acknowledged. Consider, for example, that while a photograph can be readily altered to a limited extent, it can be authenticated only to some degree by comparing a positive print with its negative film recorded by a camera while inspecting the negative film for evidence of physical alteration. Authentication of an image recorded by a digital camera is more difficult because there is no physical "original" to compare or negative to examine; furthermore, the digital image file produced by these cameras (as well as other digitally recorded information such as audio and video files) can be easily manipulated using sophisticated computers which make such manipulation easy and, as techniques improve, more difficult to detect.
Today, most pictures that appear in newspapers and magazines have been altered to some degree, with the severity varying from the trivial (such as deliberately removing distracting background while cleaning up "noise") to the point of deliberate deception, such as substituting heads on people's bodies. As the power, flexibility and ubiquity of image-altering computers continues to increase, the notion that photographs "do not lie" will become less widely held.